FM3808_06 datasheet(7/27 Pages) RAMTRON

7 / 27 page

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FM3808

Rev. 1.3 (EOL)

Feb. 2006

Page 7 of 27

system power fails, the VDD voltage will drop. When

it crosses the voltage on the VBAK supply pin, the

clock/calendar power will switch to the backup power

supply VBAK. The supervisor function, described

below, controls the switchover process as part of a

more complete power management circuit.

The following functions are powered from the backup

power source when VDD < VBAK (backup mode) :

• Clock/calendar core

• Alarm interrupt/comparator

• INT pin (determined by ABE & AIE bits);

active low only

• Flags connected to related functions

The following functions are not powered and are

disabled when VDD < VLO :

• User interface

• Watchdog timer

• Power monitor & band-gap (V

DD < ≈ 2.0V)

• Flags connected to related functions

• All FRAM access & updates

• Calibration operation

• INT pin if programmed as active-high

32.768 kHz

crystal

Oscillator

Clock

Divider

Update

Logic

32 Hz

512 Hz

Seconds

7 bits

Minutes

7 bits

Hours

6 bits

Date

6 bits

Months

5 bits

Years

8 bits

Days

3 bits

User Interface Registers

1 Hz

Figure 2. Real-Time Clock Core Block Diagram

FM3808 数据表(PDF) 7 Page - Ramtron International Corporation

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